Heat-regenerator



L. B. SKINNER.

HEAT REGENEHATOR.

APPLICATION FILED FEB. 10. :919.

1,350,267'. Patented Aug. 17,1920.`

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UNITED STATES LEWIS BAILEY SKINNER, OF DENVER, COLORADO.

Specification of Letters Patent.

Patented Aug. 17, 1920.

Application led February 10, 1919. Serial No. 276,126.

To all whom t may concern Be it known that I, LEWIS B. SKINNER, acitizen of the United States, residin at Denver, in the county of Denverand l tate of Colorado, have invented certain new and usefulImprovements in Heat-Regenerators; and I do hereby declare .thefollowing to be a full, clear, and exact description of the invention,such as will enable others skilled in the art to which it appertainsto-Inake and use the same.

This invention relates to heat regenerators and it relates moreparticularly to metallurgical apparatus comprising a reverberatoryfurnace adapted for smelting ores carrying volatilizable metal values,in combi-- nation with a heat regenerator or exchanger of thedouble-surface type into which hot fume-laden gases from the furnace aredischarged and throu h which they flow in heat-transferring re ation toair to be preheated for combustion in said furnace, the respective pathstraversed by said furnace gases and said air in passing through theregenerator being separated by a metal wall, protected on the sideexposed to said gases by a dense adherent coatlng of metalliferous fume.

The apparatus herein described is disclosed in my copending priorapplications Serial Nos. 216,503 and 216,594, filed February 11, 1918.

The use of hot stoves in which the air entering to be preheated ispassed throughmetal pipes (usuall of iron) around which l hot gasesescaping rom a metallurgical furthan the temperature at whichdestruction of the metal would begin to occur can be used Without damageto the separating walls.

AI have discovered that when highly heated fumes carrying volatilecompounds of metals are brought into Contact with metallic surfacesthere is deposited on the metal a tenacious coating of condensed fumewhich coating is sufiicient in thickness to protect the metal both fromoxidation and, by reason of its lower heat conductivity, from excessiveheating. This coating tenaciously adheres to a thickness sufficient tothoroughl protect the metal; but if it be exposed urther to gasescarrying metalliferous fume, said coating does not continue to build upin thickness beyond a fairly well definable limit which is insuflicientvto destroy the practical efficiency of the metal as regards heattransference. This is du@ to the ila that the adhesion of the condensedfume to metal is much more tenacious than its adhesion to previouslydeposited fume. Therefore the buiding up process proceeds until acertain thickness of fume has accumulated; beyond which there is nomaterial accretion because if more fume is condensed on the surfaces itwill Hake off. The tenacious protective skin of condensed fume depositedon the metal is of relatively low heat conductivity as compared to themuch greater heat conductivity of the metal which it protects. Inaccordance with the invention, advantage is taken of this fact toconstruct a heat exchanger' or regenerator in such manner that passagesare provided for hot furnace gases and for air, respectively, saidpassages being defined and separated from one another by metal Walls andthe wall surfaces adjacent the furnace gases being provided with acoatin of the character above described.

For te sake of a concrete illustration, and in order to aford a fullerunderstanding of the invention, one type of metallurgical apparatusembodying the principles of the invention is illustrated more or lessdiagrammatically in the accompanying drawlng forming a part hereof. Theapparatus here shown is particularly adapted for use in. smeltingcomplex ores containing both volatile and non-volatile metal valueswhich it is desired to separate and recover in as concentrated form aspossible. For example, the ore to be treated may contain zinc, lead,copper, and precious metals, and the object is to obtain the bulk of thezinc and lead as a fume, to concentrate the copper and precious metalsin a matte, and to separate the gangue or waste material of the ore inthe form of a slag containing but rela-. tively small amounts of metalvalues. Ac-

cording to the process set forth in my prior application Serial No.216,594, such an ore is smelted under proper conditions, in arevrrlnrratory furnace lired with preheated blast. the furnacetemperature normally being 121)()O C. or above. The present apparatasImakes possible the use of the heavily fume-laden gases at theseextremely high temperatures to preheat air for the hot blast. somethingof which no prior apparatus is capable so far as l am aware. The use ofthe Siemens type of regenerator in which brick checker work is employed,is impossible with the type of fume-laden furnace gases here inquestion, because the checker work would soon become clogged with fumeand inoperative; and it has naturall y been assumed that metal stoves ofthe double surface type would be destroyed if exposed to said gases attemperatures exceeding the softening point of the metal. The discoverythat such metal stoves could be utilized in this connection whenprovided with a protective skin of condensed fume, constitutes,therefore, an important practical advance in this art.

Referring to the drawing, 1 represents a reverberatory furnace providedwith hoppers for charging in ore, and also provided with firing meanscomprising a conduit 2 for furnishing preheated air for-combustion ofpowdered coal supplied through the coal dust hopper, all as shown. Aby-pass 3, valved at 4, provides means for controlling the character ofthe combustion in the furnace. Hot gases laden with a fume consistingchiey of more or less oxidized zinc and lead are conducted from thefurnace through conduit 5, and are normally discharged through valve 6into the heat exchange chamber 7 of the regenerator device. Considerablefume may drop out of the gases and collect on the bottom of the chamber,being removed from time to time in any suitable manner without difculty.A by-pass 8, valved at 9, is provided whereby the gases may betemporarily conducted around the regenerator chamber if desired. Fromthe chamber 7 or the by-pass 8 as the casemay be, the gases from thefurnace go through an air cooler or a long conduit, as desired, to a baghouse 10 provided with a plurality of fabric bags 11 into whichthe gasesare discharged and which allow the escape of the products of combustionbut arrest condensed metallic fume in t'he customary manner, sucharrested fume being removable as desired through the fume dischargeshown.

The heat exchanger or regenerator here illustra-ted is of the doublesurface type;

.that is to say, it is a regenerative stove through which the heatinggases always flow by the same condults or passages, and

the air which is being heated likewise always follows the same path,which latter path is separate and distinct from that of the furnacegases and is separated therefrom by a metal wall. In-the presentexample, the heating gases follow the passages in the chamber 7 betweenbends or coils 14 of iron pipe through which air to be preheated forcombustion is conducted, the cool air being supplied through pipel tosaid coilsby any suitable means, such as the blower 12. For convenience,a by-pass 15, controlled by valve 16, is provided whereby a part of theair may be b v-passed around the stove if it is desired at any time tolower the temperature of the air for combustion., As stated, the pipes14 are of iron, and iron begins to soften at temperatures in thevicinity of 1000o C., and is also destructively oxidized if unprotected.As the temperature in the reverberatory furnace is upward of 1200o C.,and may be 1300o C., or more, and since the fume-laden gases dischargedinto the heat exchanger are not at a much lower temperature, beinggenerally at 10000 C., or above, unprotected iron pipes would obviouslynot withstand the conditions prevailing in the heat exchange chamber forany considerable time. The iron pipes are therefore protected in themanner characteristic of the invention. For example, before subjectingthe pipe bends 14 to the full heat of the furnace gases, the furnace maybe run at a reduced rate, or in some other way the temperature in theheat exchange chamber may be kept below the danger point, until ,fumecarried into the chamber by the furnace gases has condensed on the pipebends and built up a protecting layer of oxidized zinc and lead to anecessary extent, after which the furnace may be brought to full heat.By way of illustration, let it' be assumed that the metal of the ironpipes itself is one inch in thickness, and that the built-on protectinglayer of fume thus formed is also one inch thick. If the fume has sayone-tenth of the heat conductivity of the iron, and `if t'he fumeladengases have a temperature of 120Go or 13000 C., when the furnace isoperating normally, it is evident that by passing cool air through thepipes in proper quantity the air will abstract heat rapidly enough fromthe iron pipe to keep its temperature materally below the danger point,this danger pointbeing attained only at some locality beyond the outersurface of the iron pipe and Within the adherent rotecting layer offume. By utilizing a su` cient length of metal pipe and continuouslycirculating air therethrough, it is feasible to reheat this air to atemperature of 500 or above, without endangering the Vstructuralintegrity of the heat exchanger. The combination of vto such aregenerator with a reverberat'ory furnace therefore makes it possiblefor the rst time to treat ores of the character described at hightemperatures in a reverberatory furnace in an efficient and economicalmanner.

Instead of initially operating the furnace at a reduced rate, anothermethod, which does not involve delay in bringing the furnace up to fullheat, may be adopted for providing the heat exchanger pipes with a denseprotective coating of fume. This consists in preliminarily protectingthe pipes by more or less temporary covering means of some kind, thetemporary covering means being most desirabl of such nature as todisintegrate gradua ly during the eatingup operation, and to beeventually replaced wholly or in part by the dense metalliferous fumecoating already described. For example, I may mechanically coat or smearthe pipes, especially those at the end of the regenerator nearest thefurnace, with clay mud; or tire clay sleeves may be dropped over thesepipes. With the .pipes thus temporarily protected, the furnace may bebrought up to full heat quickly. The protective layer provided by themud coating or the fireclay sleeves, as the case may be, ultimatelycracks at the high temperatures involved, and peels od or falls off butonly rather gradually. That is, it breaks away progressively indifferent spots enabling the iron of the pipes tov conduct lthe heataway from the successivelyexposed surfaces fast enough to preventsubstantial damage. In the meantime, the exposed surfaces becomepermanently coated with a dense adherent layer of condensed fume, whichreplaces part or eventually all of the mechanically applied covering.

By means of the described apparatus, therefore. it is possible toeffectively preheatthe'air for combustion under the conditionsldescribed, that is, to employ a double surface hot stove type of heatexchange!" with fume-laden furnace gases at a temperature which may beconsiderably above that at which the metal of the stove would soften orbe seriously damaged, While at the same time there is no stoppage offurnace o eration by reason of fume and dust lo ging Within the heatexchanger and `rendering it inoperative. A

What I claim is:

1. Metallurgical apparatus comprising the combination, with ametallurgical furnace, of a heat regenerator having passages forconducting to and for conducting from said furnace, respectively, saidpassa s be- 6() ing defined .and separated by a meta Wall, and the wallsurface next the furnace gases being provided with an adherentprotective coating of condensed metalliferous fume.

2. Metallurgical apparatus comprising the combination, with areverberatory furnace, of a heat regenerator comprising a chamber intowhich ases are dlschar ed from said furnace, an a metal conduit isposedin said chamber and arranged to con-* duct air for combustion throughsaid chamber for supply to said furnace, said conduit having its outersurface protected by a metalliferous fume coating of lower heatconductivity than the metal of the conduit.V

3. Metallurgical apparatus comprising the combination, withareverberatory furnace, of a heat regenerator comprising a chamber intowhich ases are discharged from said furnace, an air-preheating coils orbends of iron pipe disposed in said chamber and provided externally witha dense adherent coating of zinc-lead fume.

4. Metallurgical apparatus comprising the combination, with areverberatory fur- 85 nace, of a heat regenerator com rising a chamberinto which ases are discharged from said furnace, an air-preheatingcoils or bends of iron pipe disposed in said chamber and providedexternally with a dense adherent coating of zinkiferous fume.

5. Metallurgical apparatus comprising the combination with areverberatory furnace, of a heat regenerator having passages forconducting alr to'and for conducting 95 gases from' said furnace,respectively, said passages being defined and se arated by a. metal\vall,`and the wall sur ace next the furnace gases being provided withan adherent protective coatlng of condensed metalliferous fume.

In testimony whereof I hereunto aflx my signature.

\ LEWIS BAILEY SKIN N ER.

